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What is the difference between a molecular formula and an empirical formula?
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molecule
Several methods of representing a molecule's structure. In Lewis structures, element symbols represent atoms, and dots represent electrons surrounding them. A pair of shared electrons (covalent bond) may also be shown as a single dash. The ball-and-stick model better illustrates the spatial arrangement of the atoms. For aromatic compounds, the Kekulé structure is common, in which each bond is represented by a dash, carbon atoms are implied where two or more lines meet, and hydrogen atoms are usually omitted. Bond-line formulas, similar to the Kekulé structure, are often used for complex nonaromatic organic compounds. Sugars are often drawn as Fischer projections, in which the carbon “backbone” is drawn as a straight vertical line, with carbon atoms implied where horizontal lines intersect the vertical one.
The primary difference between a molecular formula and an empirical formula lies in how they represent the composition of a chemical compound.1
- Empirical Formula: This formula shows the simplest whole-number ratio of the elements present in a compound. It is often used for substances that do not consist of discrete molecules, such as ionic compounds like sodium chloride, or when the molecular structure is undetermined.21
- Molecular Formula: This formula specifies the exact number and kind of every atom present in a single molecule of a substance. While different compounds can share the same empirical formula—such as ethylene and propylene, which both have the empirical formula —their molecular formulas uniquely identify their specific atomic composition (e.g., and ).1
In some instances, such as with water, the empirical and molecular formulas may be identical.1